Blair Holt, a popular 16-year-old honor student at Julian High School, pushed a friend down in her seat as shots were fired. Moments later, he was fatally shot in the abdomen.
Michael "Mario" Pace, 18, could have served life in prison for his role in the May 10, 2007, killing.
For the first time, surveillance video from the bus was released Monday. The video shows the gunman storming onto the bus, his weapon raised in the air. He immediately starts firing. A second shot shows people diving to the floor to get out of the way of the bullets.
"I didn't want to see it. I didn't want to see it. But in my heart, that was my baby," Holt's mother, Annette, said after leaving the courtroom.
Pace pleaded guilty last month to two counts of first-degree murder and two counts of aggravated battery. The judge said there was little room for mercy in the sentencing. But his attorney said Pace's extremely low IQ -- just above the legal definition of retardation -- should have figured more prominently in the sentence.
"Michael's severe, lifelong learning disability was not given the appropriate consideration that I would have hoped for," his attorney said.
Holt's father has become an outspoken community activist since Blair's murder. After court, he vowed the fight to stop street violence will go on.
"Our fight will remain visible, vigilant and vocal," he said.
Kevin Jones, the 17-year-old accused of supplying Pace with the .40-caliber gun used in the shootings, already has been sentenced to 10 years in prison after pleading guilty to conspiracy to commit murder.
Holt died shielding his friend Tiara Reed when Pace, a reputed gang member, stormed a CTA bus at 103rd and Halsted and began shooting, trying to strike a rival. Holt, 16, was not the intended target.
Reed was shot in the foot. Three others were injured.